Ocean Acidification: What is it and why should we care?

Written by Haley Zerobnick, ESLLC 2017-2018

Since the Industrial Revolution in the late 18th– early 19th century, humans as a whole have been producing more and more carbon dioxide due to the burning of fossil fuels. This excess of carbon dioxide leads to a multitude of environmental issues, one of them being the increase in acidity of the oceans on a global scale. Acidity is measured on a pH scale, pH is defined as the potential to create charged hydrogen atoms (ions). 30-40% of the carbon dioxide in the atmosphere is absorbed into the ocean while the rest remains in the air. This CO2 reacts with sea water to form carbonic acid. This acid then breaks down into a bicarbonate ion and further breaks down into a carbonate ion. The Carbonic acid is broken down by the release of hydrogen ions. These hydrogen ions are what increases the pH of the ocean. The chemical reaction looks a bit like this:

CO2 + H2O à H2CO3 (Carbonic Acid)à CO3 -2 (Carbonate ion) + 2H+ (Hydrogen ions)

Globally, the ocean is slightly alkaline with a pH of 8.25, but over the past 100 years or so, the pH has decreased to about 8.14. Although this doesn’t seem like a big difference, the pH scale is logarithmic (increases by a factor of 10) which means there has been a 30% average increase in acidity. So, the real question is why does this change matter, and what does ocean acidification affect?

Animals with exoskeletons such as crabs, mollusks, and lobsters use a compound called calcium carbonate to create their shells. To form calcium carbonate, a calcium ion bonds with a carbonate ion, but the rampant hydrogen ions rapidly form with the carbonate in the water which makes calcium carbonate harder to come by. These animals have a more difficult time creating strong shells that will protect them from predators. If the ocean becomes acidic enough, these shells will start to dissolve completely. Other organisms that use calcium carbonate to grow are corals. Without coral, entire ecosystems will be wiped out. Single-celled organisms also use calcium carbonate. These organisms make up the base of the food chain and without them, entire populations will disappear. Historically, these increases in acidity are marked with huge extinctions and in order to prevent this from happening in the near future, carbon dioxide emissions need to be drastically reduced.

Picture1

This picture shows the results of acidification over a time period of 45 days.

A helpful video: https://www.youtube.com/watch?v=GL7qJYKzcsk

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